Gas metal arc welding, commonly referred to as "GMAW" or "MIG" welding, is an electric arc welding process in which the arc is shielded from the ambient atmosphere by a gas or a mixture of gases. Metal is transferred to a workpiece through the arc from a consumable wire electrode. The consumable wire electrode is continuously fed into the arc at a preselected speed corresponding to a given deposition rate for a given wire size.
The optimum type of metal transfer employed with the gas metal arc process is a spray arc where fine metal droplets are transferred in a very controlled manner across the arc gap. Very little spatter is produced using this welding technique. The type of metal transfer can be obtained only with a certain combination of shielding gases and welding parameters and thus is generally produced only within a fairly narrow range of conditions.
Heretofore gas metal arc welding shielding gases have comprised solely carbon dioxide or have comprised mixtures of argon, oxygen, carbon dioxide or helium. Each heretofore known shielding gas has a specific known range within which the process with that gas will perform acceptably well. Helium, if employed in the gas mixture, is present in a concentration exceeding 50 percent and is used to impart special characteristics to the weld but only when its high cost can be justified.
While the use of the high cost helium shielding gas mixtures may be acceptable in the welding of certain specialty metals such as stainless steels, the cost of such gas mixtures is usually prohibitive for use in welding carbon or alloys steels.
Accordingly, it is an object of this invention to provide an improved gas metal arc welding process which can employ a shielding gas which does not require the presence of a large concentration of helium and yet achieves a comparable improvement in desired weld characteristics.
It is another object of this invention to provide an improved gas metal arc welding process which can employ a shielding gas which does not require the presence of oxygen.
It is yet another object of this invention to provide an improved gas metal arc welding process which can effectively weld carbon and low alloy steels at greater efficiency, and hence lower cost, than heretofore available processes.